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प्रश्न
विकल्प
40 cm
25 cm
`1/40` cm.
`1/25` cm
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उत्तर
The power of a convex lens is 2.5 dioptres. Its focal length is 40 cm.
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संबंधित प्रश्न
To determine the approximate focal length of the given convex lens by focussing a distant object (say, a sign board), you try to focus the image of the object on a screen. The image you obtain on the screen is always
(a) erect and laterally inverted
(b) erect and diminished
(c) inverted and diminished
(d) virtual, inverted and diminished
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
Draw a ray diagram to show the formation of the image of an object be placed so that a real and inverted image of the same size as the object is obtained using a convex lens
The diagram given alongside shows a ray of light entering a rectangular block of glass.
- Copy the diagram and draw the normal at the point of entry.
- Draw the approximate path of the ray of light through the glass block and out of the other side.
If the image formed by a convex lens is of the same size as that of the object, what is the position of the image with respect to the lens?
Define the principal axis of a convex lens.
Describe with the help of a ray-diagram, the size, nature and position of the image formed by a convex lens when an object is placed beyond 2f in front of the lens.
A convex lens has a focal length of 10 cm. At which of the following positions should an object be placed so that this convex lens may act as a magnifying glass?
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
Which of the object distances gives the biggest image?
What type of images can a convex lens make?
How would a pencil look like if you saw it through a convex lens? (Assume the pencil is close to the lens). Is the image real or virtual?
What kind of lens can form:
an inverted diminished image?
An image formed on a screen is three times the size of the object. The object and screen are 80 cm apart when the image is sharply focussed.
- State which type of lens is used.
- Calculate focal length of the lens.
A lens forms an erect, magnified, and virtual image of an object.
- Name the type of lens.
- Draw a ray diagram to show the formation of the image.
- Where is the object placed in relation to the lens?
- Name the device which uses this principle.
The focal length of a lens is positive. In this case, state the kind of lens.
State the position of object, position of image, nature of image when: Convex lens is used in cine projector.
State the position of object, position of image, nature of image when: Convex lens is used in observing biological specimens.
Write the three characteristics of the image formed by a convex lens of focal length 20 cm for the object at distance (i) 10 cm, (ii) 30 cm, (iii) 40 cm, (iv) 60 cm from the lens.
: Object near the lens : : ______ : 
Distinguish between Concave lens and Convex Lens.
